Vulnerability Database

346,508

Total vulnerabilities in the database

CVE-2021-0251 — juniper / junos

NULL Pointer Dereference

A NULL Pointer Dereference vulnerability in the Captive Portal Content Delivery (CPCD) services daemon (cpcd) of Juniper Networks Junos OS on MX Series with MS-PIC, MS-SPC3, MS-MIC or MS-MPC allows an attacker to send malformed HTTP packets to the device thereby causing a Denial of Service (DoS), crashing the Multiservices PIC Management Daemon (mspmand) process thereby denying users the ability to login, while concurrently impacting other mspmand services and traffic through the device. Continued receipt and processing of these malformed packets will create a sustained Denial of Service (DoS) condition. While the Services PIC is restarting, all PIC services will be bypassed until the Services PIC completes its boot process. An attacker sending these malformed HTTP packets to the device who is not part of the Captive Portal experience is not able to exploit this issue. This issue is not applicable to MX RE-based CPCD platforms. This issue affects: Juniper Networks Junos OS on MX Series 17.3 version 17.3R1 and later versions prior to 17.4 versions 17.4R2-S9, 17.4R3-S2; 18.1 versions prior to 18.1R3-S9; 18.2 versions prior to 18.2R3-S3; 18.3 versions prior to 18.3R3-S1; 18.4 versions prior to 18.4R3; 19.1 versions prior to 19.1R2-S2, 19.1R3; 19.2 versions prior to 19.2R2; 19.3 versions prior to 19.3R3. This issue does not affect: Juniper Networks Junos OS versions prior to 17.3R1.

  • Published: Apr 22, 2021
  • Updated: Nov 16, 2025
  • CVE: CVE-2021-0251
  • Severity: High
  • Exploit:

CVSS v3:

  • Severity: High
  • Score: 8.6
  • AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

CVSS v2:

  • Severity: Medium
  • Score: 5
  • AV:N/AC:L/Au:N/C:N/I:N/A:P

CWEs:

Software From Fixed in
juniper / junos 17.3-r1 17.3-r1.x
juniper / junos 17.3-r2 17.3-r2.x
juniper / junos 17.3-r2-s2 17.3-r2-s2.x
juniper / junos 17.3-r3 17.3-r3.x
juniper / junos 17.3-r1-s4 17.3-r1-s4.x
juniper / junos 17.3-r3-s1 17.3-r3-s1.x
juniper / junos 17.3-r3-s2 17.3-r3-s2.x
juniper / junos 17.3-r2-s1 17.3-r2-s1.x
juniper / junos 17.3-r3-s3 17.3-r3-s3.x
juniper / junos 17.3-r3-s4 17.3-r3-s4.x
juniper / junos 17.3-r3-s5 17.3-r3-s5.x
juniper / junos 17.3-r3-s6 17.3-r3-s6.x
juniper / junos 17.3-r2-s3 17.3-r2-s3.x
juniper / junos 17.3-r1-s1 17.3-r1-s1.x
juniper / junos 17.3-r2-s4 17.3-r2-s4.x
juniper / junos 17.3-r3-s7 17.3-r3-s7.x
juniper / junos 17.3-r2-s5 17.3-r2-s5.x
juniper / junos 17.3-r3-s8 17.3-r3-s8.x
juniper / junos 17.3-r3-s9 17.3-r3-s9.x
juniper / junos 17.3-r3-s10 17.3-r3-s10.x
juniper / junos 17.4-r3-s1 17.4-r3-s1.x
juniper / junos 17.4-r2-s8 17.4-r2-s8.x
juniper / junos 17.4-r2-s5 17.4-r2-s5.x
juniper / junos 17.4-r2-s6 17.4-r2-s6.x
juniper / junos 17.4-r2-s7 17.4-r2-s7.x
juniper / junos 17.4-r1-s7 17.4-r1-s7.x
juniper / junos 17.4-r1-s4 17.4-r1-s4.x
juniper / junos 17.4-r2-s3 17.4-r2-s3.x
juniper / junos 17.4-r2-s4 17.4-r2-s4.x
juniper / junos 17.4-r1-s6 17.4-r1-s6.x
juniper / junos 17.4-r1-s5 17.4-r1-s5.x
juniper / junos 17.4-r1-s2 17.4-r1-s2.x
juniper / junos 17.4-r3 17.4-r3.x
juniper / junos 17.4-r2-s1 17.4-r2-s1.x
juniper / junos 17.4 17.4.x
juniper / junos 17.4-r1-s3 17.4-r1-s3.x
juniper / junos 17.4-r2-s2 17.4-r2-s2.x
juniper / junos 17.4-r1-s1 17.4-r1-s1.x
juniper / junos 17.4-r1 17.4-r1.x
juniper / junos 17.4-r2 17.4-r2.x
juniper / junos 18.1-r1 18.1-r1.x
juniper / junos 18.1-r3 18.1-r3.x
juniper / junos 18.1-r2 18.1-r2.x
juniper / junos 18.1-r3-s4 18.1-r3-s4.x
juniper / junos 18.1-r3-s3 18.1-r3-s3.x
juniper / junos 18.1-r3-s2 18.1-r3-s2.x
juniper / junos 18.1 18.1.x
juniper / junos 18.1-r2-s1 18.1-r2-s1.x
juniper / junos 18.1-r2-s4 18.1-r2-s4.x
juniper / junos 18.1-r2-s2 18.1-r2-s2.x
juniper / junos 18.1-r3-s1 18.1-r3-s1.x
juniper / junos 18.1-r3-s5 18.1-r3-s5.x
juniper / junos 18.1-r3-s6 18.1-r3-s6.x
juniper / junos 18.1-r3-s7 18.1-r3-s7.x
juniper / junos 18.1-r3-s8 18.1-r3-s8.x
juniper / junos 18.2-r3-s2 18.2-r3-s2.x
juniper / junos 18.2-r3-s1 18.2-r3-s1.x
juniper / junos 18.2-r2-s7 18.2-r2-s7.x
juniper / junos 18.2-r1-s2 18.2-r1-s2.x
juniper / junos 18.2-r2-s5 18.2-r2-s5.x
juniper / junos 18.2-r2-s6 18.2-r2-s6.x
juniper / junos 18.2-r1-s4 18.2-r1-s4.x
juniper / junos 18.2-r1-s5 18.2-r1-s5.x
juniper / junos 18.2-r2 18.2-r2.x
juniper / junos 18.2-r3 18.2-r3.x
juniper / junos 18.2-r1 18.2-r1.x
juniper / junos 18.2-r2-s3 18.2-r2-s3.x
juniper / junos 18.2-r2-s4 18.2-r2-s4.x
juniper / junos 18.2 18.2.x
juniper / junos 18.2-r2-s1 18.2-r2-s1.x
juniper / junos 18.2-r2-s2 18.2-r2-s2.x
juniper / junos 18.2-r1-s3 18.2-r1-s3.x
juniper / junos 18.3-r1-s1 18.3-r1-s1.x
juniper / junos 18.3-r2 18.3-r2.x
juniper / junos 18.3-r1 18.3-r1.x
juniper / junos 18.3-r1-s2 18.3-r1-s2.x
juniper / junos 18.3 18.3.x
juniper / junos 18.3-r1-s4 18.3-r1-s4.x
juniper / junos 18.3-r1-s3 18.3-r1-s3.x
juniper / junos 18.3-r2-s3 18.3-r2-s3.x
juniper / junos 18.3-r1-s5 18.3-r1-s5.x
juniper / junos 18.3-r2-s1 18.3-r2-s1.x
juniper / junos 18.3-r2-s2 18.3-r2-s2.x
juniper / junos 18.3-r1-s6 18.3-r1-s6.x
juniper / junos 18.3-r3 18.3-r3.x
juniper / junos 18.3-r2-s4 18.3-r2-s4.x
juniper / junos 18.4-r2-s4 18.4-r2-s4.x
juniper / junos 18.4-r2-s3 18.4-r2-s3.x
juniper / junos 18.4-r1-s6 18.4-r1-s6.x
juniper / junos 18.4-r2-s2 18.4-r2-s2.x
juniper / junos 18.4-r2-s1 18.4-r2-s1.x
juniper / junos 18.4-r2-s5 18.4-r2-s5.x
juniper / junos 18.4-r2-s6 18.4-r2-s6.x
juniper / junos 18.4-r1-s7 18.4-r1-s7.x
juniper / junos 18.4-r1-s1 18.4-r1-s1.x
juniper / junos 18.4-r1-s3 18.4-r1-s3.x
juniper / junos 18.4-r1-s4 18.4-r1-s4.x
juniper / junos 18.4-r1-s2 18.4-r1-s2.x
juniper / junos 18.4-r2 18.4-r2.x
juniper / junos 18.4-r1-s5 18.4-r1-s5.x
juniper / junos 18.4 18.4.x
juniper / junos 18.4-r1 18.4-r1.x
juniper / junos 19.1-r1-s1 19.1-r1-s1.x
juniper / junos 19.1-r1-s3 19.1-r1-s3.x
juniper / junos 19.1-r1-s2 19.1-r1-s2.x
juniper / junos 19.1-r1 19.1-r1.x
juniper / junos 19.1 19.1.x
juniper / junos 19.1-r1-s5 19.1-r1-s5.x
juniper / junos 19.1-r1-s4 19.1-r1-s4.x
juniper / junos 19.1-r2 19.1-r2.x
juniper / junos 19.1-r2-s1 19.1-r2-s1.x
juniper / junos 19.2-r1-s4 19.2-r1-s4.x
juniper / junos 19.2 19.2.x
juniper / junos 19.2-r1-s3 19.2-r1-s3.x
juniper / junos 19.2-r1-s5 19.2-r1-s5.x
juniper / junos 19.2-r1-s1 19.2-r1-s1.x
juniper / junos 19.2-r1-s2 19.2-r1-s2.x
juniper / junos 19.2-r1 19.2-r1.x
juniper / junos 19.3-r2 19.3-r2.x
juniper / junos 19.3 19.3.x
juniper / junos 19.3-r1 19.3-r1.x
juniper / junos 19.3-r2-s2 19.3-r2-s2.x
juniper / junos 19.3-r2-s1 19.3-r2-s1.x
juniper / junos 19.3-r1-s1 19.3-r1-s1.x
juniper / junos 19.3-r2-s3 19.3-r2-s3.x
juniper / junos 19.3-r2-s4 19.3-r2-s4.x
juniper / junos 19.3-r2-s5 19.3-r2-s5.x

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.